The present invention relates to an apparatus with a receiver for receiving tire condition signals. More particularly, the present invention relates to an apparatus with a vehicle-based receiver for receiving both tire condition signals and convenience function signals.
A vehicle-based receiver receives a convenience function signal from a portable transmitter referred to as a fob and, in response to the convenience function signal, controls performance of a convenience function, such as locking or unlocking a vehicle door. The vehicle-based receiver also can receive a tire condition signal from a tire condition monitor and, in response to the tire condition signal, can control the display to indicate a sensed tire condition. The vehicle-based receiver includes a detector circuit for demodulating the convenience function signal and the tire condition signal. The detector circuit of the receiver includes a comparator that compares a carrier signal, after some initial processing, to a threshold value. The threshold value is dependent upon a time constant of the detector circuit.
The fob, which transmits the convenience function signal, is typically stationary or moving at a relatively low speed relative to the vehicle-based receiver when the convenience function signal is transmitted from the fob. As a result, the amplitude of the carrier signal for digital true values (i.e., ones) of an amplitude shift keyed message packet remains relatively constant throughout the transmission of the convenience function signal. The convenience function signal also includes a dead time between a preamble or wake-up portion and an identification portion of the convenience function signal. The dead time allows the receiver to xe2x80x9cwake-upxe2x80x9d from a low power consumption mode. As a result of the relatively constant amplitude and the dead time of the convenience function signal, a long time constant is desired for the detector circuit of the receiver that receives the convenience function signal.
Conversely, the tire condition monitor, which is fixedly mounted within a tire, may be moving at a relatively high speed, during tire rotation, relative to the receiver when the tire condition signal is transmitted. The amplitude of the carrier signal varies as a function of the distance between the transmitting tire condition monitor and the receiver during the transmission of the tire condition signal. As a result, the amplitude of the carrier signal for digital true values of the received amplitude shift keyed message packet varies because the distance changes during the transmission of the tire condition signal. Additionally, during operation of the vehicle, the tire condition signal does not include a dead time portion. As a result of the varying amplitude and no dead time of the tire condition signal, a shorter time constant, relative to the desired convenience function time constant, is desired for the detector circuit of the receiver that receives the tire condition signal.
A receiver for receiving both the convenience function signal and the tire condition signal that is designed with a fixed time constant would be only moderately sensitive to the convenience function signal and only moderately sensitive to the tire condition signal.
In accordance with an exemplary embodiment of the present invention, an apparatus is provided. An apparatus comprises a controller for receiving a control parameter. At least one tire condition sensor is also provided for sensing a tire condition and for transmitting a tire condition signal indicative of the sensed tire condition. A receiver is provided for receiving the tire condition signal and for comparing the received tire condition signal to a changeable threshold to output a digital signal indicative of the received tire condition signal. The changeable threshold changes at time intervals determined by a time constant of the receiver. The time constant of the receiver is variable. The controller is operatively connected to the receiver and varies the time constant of the receiver in response to the received control parameter.
In accordance with a second aspect of the present invention, an apparatus comprises at least one tire condition sensor for sensing a tire condition and for transmitting a tire condition signal indicative of the sensed tire condition. The apparatus also comprises a convenience function transmitter for transmitting a convenience function signal requesting performance of a convenience function. A display device is operable for displaying the sensed tire condition. A function device is actuatable for performing the convenience function. A vehicle-based receiver receives signals including the tire condition signal and the convenience function signal. The receiver has a variable time constant and outputs digital signals indicative of the received signals. A controller is operatively connected to the display device and the function device. The controller receives the digital signals from the receiver. The controller, in response to the received digital signals, controls the display device and the function device.